Improving coal gasification and synfuel production?
An outline for a more energy and cost efficient coal gasification and synfuel production facility has been put forward by a team of researchers at the University of Padova in Italy.
The proposed facility is based on integrated gasification combined cycle (IGCC) and Fischer-Tropsch synfuel production using syngas from a dual bed gasification system. However, the team has suggested that combustion and gasification be carried out in separate fluidised bed reactors, with an inert solid, such as sand, transferring heat between them. This would enable combustion using regular air instead of pure oxygen, which is expensive to produce but is normally required to maintain the temperature in gasification reactors so endothermic reactions can occur.
‘This system is not new, as there are pilot plants of this type in the world, but they use only biomass and not coal,’ says Maria Sudiro, a graduate student at Padova who worked on the study. The proposed facility also saves energy, as it could gasify at temperatures of 850ºC, lower than other facilities which operate at up to 1,000ºC. ‘Our work is interesting because, for the first time, results of this simulated scheme have been modelled and an immediate comparison [with working electric and synfuel plants] was made.’
In simulations, the efficiency of the IGCC process is said to have increased by 27.9%, with 21.8% less CO2 emissions, while coal-to-liquid energy efficiency increases by 71.1%, with 31.9% fewer emissions.
However, these figures have been questioned by Dr Colin Henderson of the IEA Clean Coal Centre in London, UK, who notes that conventional IGCC already has an efficiency of around 40-43% on a lower heating value basis, although he concedes the CO2 emissions of the Padova process look promising.
‘Fluidised bed pyrolysis of coal has been demonstrated at pilot scale only, [and] syngas filtration at 850ºC is also not demonstrated,’ he says. ‘The concept is still some way from competing with conventional gasification.’